In the case of taking pictures or video underwater, a camera or video camera is housed in a water proof housing arranged with an imaging transparent window in a position facing a lens surface of an imaging lens of a camera of video camera. Because the water pressure on the water proof housing increases as the depth of the water increases, there is a demand for pressure resistant sealing in the water proof housing which houses the video camera. For example, a titanium alloy high strength metal cylinder is used as a water proof housing which has this type of pressure resistant sealing. It is necessary to arrange a transparent window for imaging in the position which faces the lens surface of the imaging lens even in a water proof housing used deep underwater, and a parallel flat plate or dome shaped acrylic plate or glass plate is used as a window with a thickness which can withstand a certain water pressure. Furthermore, here a lens surface refers to a surface perpendicular to a light axis with respect to the rotation symmetrical axis of the imaging lens.
Because stress exceeding air pressure of 500 is applied in a hadal zone of 5000 m, it is not easy to manufacture a pressure resistant sealed housing which houses a camera or video camera at a practical cost. In recent years, a glass hollow sphere has been used the housing for housing electronic devices or control devices in the deep sea. This is because in an environment where a high level of stress is applied from all directions as in the deep sea, only a uniform compressive stress is applied on a glass hollow sphere and a tensile stress which causes the glass to break does not occur. Furthermore, the exchange of data or signals between electronic devices or control devices housed within the glass hollow sphere which is a sealed container is carried out by wireless communication (Japanese Examined Patent Application Publication H9-505711, Japanese Laid Open Patent H11-122518, Japanese Laid Open Patent 2005-128375, Japanese Laid Open Patent 2012-245944, http://www.jamstec.go.jp/j/about/equipment/ships/deepto.html, http://www.nichigi.co.jp/products/ocean/products/products_007.html, http://www.nishiyama.co.jp/products/s_i_machine/camera/index.html, http://www.nautilus-gmbh.com/eng/files/110524%20vitrovex_indroduction_144dpi.pdf, http://www.seatronics-group.com/assets/uploads/resources/2010/3/23ac0e35-5c5e-4e3b-9885-500ca02162cd.pdf).